Defining the properties of the multifunctional galectin family are particularly challenging, but has been facilitated by the creation of transgenic animals. In these respects, functions of broadly studied galectin-1, -3, and -9, have advanced considerably as a result of close examinations of knockout mice. While the pro-apoptotic properties of extracellular galectin-1 and -9 were determined in vitro, the spectrum of their regulatory functions in T helper cell influence was revealed by studies in galectin-1 and galectin-9 knockout (ko) mice. Both galectins were found to suppress Th1 and Th17 function by killing of these Th cells. Thus, they are both potential therapeutic agents for immune and inflammatory diseases. The functions of galectin-3 in several disease models have been explored and this protein appears to serve a pro-inflammatory role, predominantly by promoting cytokine production and infiltration of inflammatory cells, as well as prolonging inflammatory cell survival. The properties of galectin-3 as a promoter of fibrosis were confirmed as well in multiple disease models mediated by inflammatory changes. These studies support selection of galectin-3 as a therapeutic target of immune and inflammatory diseases.